Ex-situ removal of deposition on an optical element

ABSTRACT

A collector assembly with a radiation collector, a cover plate and a support member connecting the radiation collector to the cover plate are provided. The cover plate is designed to cover an opening in a collector chamber. The collector chamber opening may be large enough to pass the radiation collector and the support member. The removed radiation collector can be cleaned with different cleaning procedures, which may be performed in a cleaning device. Such cleaning device may for example consist of the following: a circumferential hull designed to provide an enclosure volume for circumferentially enclosing at least the radiation collector; an inlet configured to provide at least one of a cleaning gas and a cleaning liquid to the enclosure volume to clean at least said radiation collector; and an outlet configured to remove said at least one of said cleaning gas and said cleaning liquid from the enclosure volume.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ex-situ removal of deposition on anoptical element such as used in a lithographic apparatus.

2. Description of the Related Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.including part of one or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude steppers, in which each target portion is irradiated by exposingan entire pattern onto the target portion at one time, and scanners, inwhich each target portion is irradiated by scanning the pattern througha radiation beam in a given direction (the “scanning” direction) whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection. It is also possible to transfer the pattern from thepatterning device to the substrate by imprinting the pattern onto thesubstrate.

In a lithographic apparatus, the size of features that can be imagedonto the substrate is limited by the wavelength of the projectionradiation. To produce integrated circuits with a higher density ofdevices, and hence higher operating speeds, it is desirable to be ableto image smaller features. While most current lithographic projectionapparatus employ ultraviolet light generated by mercury lamps or excimerlasers, it has been proposed to use shorter wavelength radiation, e.g.of around 13 nm. Such radiation is termed extreme ultraviolet (EUV) orsoft x-ray, and possible sources include, for example, laser-producedplasma sources, discharge plasma sources, or synchrotron radiation fromelectron storage rings.

The source of EUV radiation is typically a plasma source, for example alaser-produced plasma or a discharge source. A common feature of anyplasma source is the production of fast ions and atoms, which areexpelled from the plasma in all directions. These particles can bedamaging to the collector and condenser mirrors which are generallymultilayer mirrors or grazing incidence mirrors, with fragile surfaces.This surface is gradually degraded due to the impact, or sputtering, ofthe particles expelled from the plasma and the lifetime of the mirrorsis thus decreased. The sputtering effect is particularly problematic forthe radiation collector. The purpose of this mirror is to collectradiation which is emitted in all directions by the plasma source anddirect it towards other mirrors in the illumination system. Theradiation collector is positioned very close to, and in line-of-sightwith, the plasma source and therefore receives a large flux of fastparticles from the plasma. Other mirrors in the system are generallydamaged to a lesser degree by sputtering of particles expelled from theplasma since they may be shielded to some extent.

In the near future, extreme ultraviolet (EUV) sources will probably usetin or another metal vapor to produce EUV radiation. This tin may leakinto the lithographic apparatus, and will be deposited on mirrors in thelithographic apparatus, e.g. the mirrors of the radiation collector. Themirrors of such a radiation collector may have a EUV reflecting toplayer of, for example, ruthenium (Ru). Deposition of more thanapproximately 10 nm tin (Sn) on the reflecting Ru layer will reflect EUVradiation in the same way as bulk Sn. It is envisaged that a layer of afew nm Sn is deposited very quickly near a Sn-based EUV source. Theoverall transmission of the collector will decrease significantly, sincethe reflection coefficient of tin is much lower than the reflectioncoefficient of ruthenium. In order to prevent debris from the source orsecondary particles generated by this debris from depositing on theradiation collector, contaminant barriers may be used. Though suchcontaminant barriers may remove part of the debris, still some debriswill deposit on the radiation collector or other optical elements.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a method for ex-situremoval of deposition on an optical element, like a radiation collectorof a lithographic apparatus.

To that end, the invention relates to a method of cleaning depositionfrom a radiation collector comprising: providing a collector chamber anda collector assembly, the collector assembly comprising a radiationcollector and a cover plate connected to the radiation collector by asupport member, and the cover plate being connected to the collectorchamber and covering a collector chamber opening such that the radiationcollector is accommodated by said collector chamber; disconnecting saidcover plate from said collector chamber; removing said collectorassembly such that said radiation collector moves out of said collectorchamber via said collector chamber opening; providing a circumferentialhull designed to circumferentially enclose at least the radiationcollector, thereby providing an enclosure volume; providing at least oneof a cleaning gas and a cleaning liquid to the enclosure volume; andremoving at least part of the deposition from at least the radiationcollector by said at least one of said cleaning gas and said cleaningliquid.

According to another aspect of the invention, the invention relates to acollector assembly comprising a radiation collector, a cover plate and asupport member connecting said radiation collector to said cover plate,said cover plate being designed to cover an opening in a collectorchamber.

According to yet another aspect, the invention relates to a systemcomprising a collector chamber and a collector assembly, the collectorchamber comprising a collector chamber opening, the collector assemblycomprising a radiation collector, a cover plate and a support memberconnecting said radiation collector to said cover plate, said coverplate being designed to cover said collector chamber opening, saidcollector chamber opening being large enough to pass said radiationcollector and the support member.

According to again another aspect, the invention relates to alithography apparatus comprising: a radiation source for generatingradiation; a collector chamber accommodating a radiation collector; acollector assembly comprising said radiation collector, a cover plateand a support member connecting said radiation collector to said coverplate, said cover plate covering an opening in said collector chamber; afirst contaminant barrier arranged between said radiation source andsaid radiation collector; a second contaminant barrier, the secondcontaminant barrier being drivingly connected to a motor; a hollow shaftfor guiding a cable from said motor to a location outside said collectorchamber not through said radiation collector; an illumination systemconfigured to condition a radiation beam derived from said radiation; asupport constructed to support a patterning device, the patterningdevice being capable of imparting the radiation beam with a pattern inits cross-section to form a patterned radiation beam; a substrate tableconstructed to hold a substrate; a projection system configured toproject the patterned radiation beam onto a target portion of thesubstrate.

According to yet another aspect, the invention relates to an assemblycomprising a collector assembly and a cleaning device, the collectorassembly comprising a radiation collector, a cover plate and a supportmember connecting said radiation collector to said cover plate, saidcover plate being designed to cover an opening in a collector chamber,said cleaning device comprising: a circumferential hull designed toprovide an enclosure volume for circumferentially enclosing at least theradiation collector; an inlet configured to provide at least one of acleaning gas and a cleaning liquid to the enclosure volume to clean atleast said radiation collector; and an outlet configured to remove saidat least one of said cleaning gas and said cleaning liquid from theenclosure volume.

According to another aspect of the invention, the invention relates to acleaning method comprising: providing a lithographic apparatus with atleast one optical component contaminated with a deposition; providing acircumferential hull designed to circumferentially enclose said opticalcomponent, thereby providing an enclosure volume; providing at least oneof a cleaning gas and a cleaning liquid to the enclosure volume; andremoving at least part of the deposition from the optical component.

According to yet another aspect of the invention, the invention relatesto a cleaning device, comprising: a circumferential hull designed toprovide an enclosure volume to circumferentially enclose at least oneoptical component; an inlet configured to provide at least one of acleaning gas and a cleaning liquid to the enclosure volume; and anoutlet configured to remove at least said one of said cleaning gas andsaid cleaning liquid from the enclosure volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying schematic drawings inwhich corresponding reference symbols indicate corresponding parts, andin which:

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the present invention;

FIG. 2 schematically depicts a side view of an EUV illumination systemand projection optics of a lithographic projection apparatus accordingto FIG. 1;

FIG. 3 schematically depicts a cross section through a source collectormodule;

FIG. 4 schematically depicts a cross section through an alternativesource collector module;

FIGS. 5 a, 5 b, and 5 c show different possible contaminant barriers;

FIG. 6 schematically depicts a cross section through a furtheralternative source collector module;

FIGS. 7 a, 7 b show different 3D views on a collector chamber and acollector assembly;

FIGS. 8 a, 8 b and 8 c schematically depict different optional cleaningdevices;

FIG. 9 shows a radiation collector with some filaments; and

FIG. 10 shows a radiation collector with a temperature controller.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus 1 according to anembodiment of the present invention. The apparatus 1 includes a sourceSO for generating radiation, an illumination system (illuminator) ILconfigured to condition a radiation beam B (e.g. UV radiation or EUVradiation) from the radiation received from source SO. The source SO maybe provided as a separate unit. A support (e.g. a mask table) MT isconfigured to support a patterning device (e.g. a mask) MA and isconnected to a first positioning device PM configured to accuratelyposition the patterning device MA in accordance with certain parameters.A substrate table (e.g. a wafer table) WT is configured to hold asubstrate (e.g. a resist-coated wafer) W and is connected to a secondpositioning device PW configured to accurately position the substrate Win accordance with certain parameters. A projection system (e.g. arefractive projection lens system) PS is configured to project a patternimparted to the radiation beam B by patterning device MA onto a targetportion C (e.g. including one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, todirect, shape, or control radiation.

The support supports, e.g. bears the weight of, the patterning device.It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support can usemechanical, vacuum, electrostatic or other clamping techniques to holdthe patterning device. The support may be a frame or a table, forexample, which may be fixed or movable as required. The support mayensure that the patterning device is at a desired position, for examplewith respect to the projection system. Any use of the terms “reticle” or“mask” herein may be considered synonymous with the more general term“patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a reflective type (e.g. employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g. employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located, for example, between theprojection system and the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives, radiation from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation is passed from the source SO tothe illuminator IL with the aid of a beam delivery system including, forexample, suitable directing mirrors and/or a beam expander. In othercases the source may be an integral part of the lithographic apparatus,for example when the source is a mercury lamp. The source SO and theilluminator IL, together with the beam delivery system BD if required,may be referred to as a radiation system.

The illuminator IL may include an adjusting device configured to adjustthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may include various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support (e.g., mask table MT), and ispatterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which projectsthe beam onto a target portion C of the substrate W. With the aid of thesecond positioning device PW and position sensor IF2 (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioning device PM and another position sensorIF1 (e.g. an interferometric device, linear encoder or capacitivesensor) can be used to accurately position the mask MA with respect tothe path of the radiation beam B, e.g. after mechanical retrieval from amask library, or during a scan. In general, movement of the mask tableMT may be realized with the aid of a long-stroke module (coarsepositioning) and a short-stroke module (fine positioning), which formpart of the first positioning device PM. Similarly, movement of thesubstrate table WT may be realized using a long-stroke module and ashort-stroke module, which form part of the second positioning devicePW. In the case of a stepper, as opposed to a scanner, the mask table MTmay be connected to a short-stroke actuator only, or may be fixed. MaskMA and substrate W may be aligned using mask alignment marks M1, M2 andsubstrate alignment marks P1, P2. Although the substrate alignment marksas illustrated occupy dedicated target portions, they may be located inspaces between target portions (these are known as scribe-lane alignmentmarks). Similarly, in situations in which more than one die is providedon the mask MA, the mask alignment marks may be located between thedies.

The depicted apparatus could be used in at least one of the followingmodes:

-   -   a. In step mode, the mask table MT and the substrate table WT        are kept essentially stationary, while an entire pattern        imparted to the radiation beam is projected onto a target        portion C at one time (i.e. a single static exposure). The        substrate table WT is then shifted in the X and/or Y direction        so that a different target portion C can be exposed. In step        mode, the maximum size of the exposure field limits the size of        the target portion C imaged in a single static exposure.    -   b. In scan mode, the mask table MT and the substrate table WT        are scanned synchronously while a pattern imparted to the        radiation beam is projected onto a target portion C (i.e. a        single dynamic exposure). The velocity and direction of the        substrate table WT relative to the mask table MT may be        determined by the (de-)magnification and image reversal        characteristics of the projection system PS. In scan mode, the        maximum size of the exposure field limits the width (in the        non-scanning direction) of the target portion in a single        dynamic exposure, whereas the length of the scanning motion        determines the height (in the scanning direction) of the target        portion.    -   c. In another mode, the mask table MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the radiation beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

The term “layer” used herein, as known to the person skilled in the art,may describe layers having one or more boundary surfaces with otherlayers and/or with other media like vacuum (in use). The term “layer”may also indicate a number of layers. These layers may be next to each,other or on top of each other, etc. They may also include one materialor a combination of materials. It should also be noted that the term“layers” used herein may, describe continuous or discontinuous layers.For example, a coating may be a layer on top of part of an opticalelement.

In the present invention, the term “material” may also be interpreted asa combination of materials. The term “deposition” herein refers tomaterial that is chemically or physically attached to a surface (e.g.the surface of an optical element), as known to the person skilled inthe art. Such deposition may be a layer, but it may also include amulti-layer structure. The deposition may include a cap layer, like aprotective coating, but it may also include undesired deposits likesputtered elemental particles from a source. The deposition may alsoinclude redeposition products or evaporation products that havedeposited. The deposition may also include a cap layer as protectionlayer including such sputtered particles, e.g. after use of an apparatuswith a source that sputters particles, or including a deposition frommaterial including one of more elements selected from the group of B, C,Si, Ge and Sn. The term “element” in the phrase “wherein the depositionincludes one or more elements selected from the group of B, C, Si, Geand Sn and combinations thereof”, refers to a deposition or cap layerincluding one or more of these elements, or including particlesincluding one or more of such elements, or including compounds (likee.g. Si or Sn oxides, Si or Sn carbides, Si or Sn nitrides, etc.)including one or more of these elements, or including alloys includingone or more of these elements, or combinations thereof (like e.g.deposition including Sn, O, C and H), as will be clear to the personskilled in the art. The phrase “deposition including one or moreelements selected from the group of B, C, Si, Ge and Sn and combinationsthereof”, may in a specific embodiment refer to a mono-layer ormulti-layers including atomic B, C, Si, Ge and Sn, or combinationsthereof. Elemental layers or nitride layers, etc., may include oxygenimpurities, as known to the person skilled in the art.

The term “halogen containing gas” or “hydrogen containing gas” refers togasses or gas mixtures including at least a halogen gas or hydrogen gas,respectively. The term “halogen” in the term “halogen containing gas”refers to at least one or more selected of F, Cl, Br and I, either as anatom (radical) or as compound, for example F₂, Cl₂, Br₂, I₂, HF, HCl,HBr, HI, interhalogen compounds, for example ClF₃, or other compoundsincluding one or more selected of F, Cl, Br and I which can be broughtinto the gas phase at a temperature between about 50-500° and which maya) either react or reduce compounds (deposition) including one or moreof B, C, Si, Ge and Sn, respectively, to elemental B, C, Si, Ge and Sn,respectively, or b) react with compounds including one or more of B, C,Si, Ge and Sn, respectively, under the formation of volatile products,or c) react with compounds including one or more of B, C, Si, Ge and Sn,respectively, under the formation of products that may form volatileproducts upon reaction with a halogen or a hydrogen, or d) react withelemental B, C, Si, Ge and Sn, respectively, to form volatile products,or e) provide halogen radicals when brought into contact with, forexample, a hot wire or a plasma (such that these radicals can react withdeposition). F₂, Cl₂, Br₂, I₂ may be used, in particular I₂. Such gassesmay further include additional components like buffer gasses, such asAr, etc. The term “halogenide” refers to, for example, binary and highercompounds of a halogen like I, Br, Cl, etc. with, for example, C, Si orGe, for example CCl₄, SiCl₄, etc.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength λ of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV or soft X-ray) radiation (e.g. having a wavelength inthe range of 5-20 nm, e.g. 13.5 nm), as well as particle beams, such asion beams or electron beams. Generally, radiation having wavelengthsbetween about 780-3000 nm (or larger) is considered IR radiation. UVrefers to radiation with wavelengths of approximately 100-400 nm. Withinlithography, it is usually also applied to the wavelengths which can beproduced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm;and/or I-line 365 nm. VUV is Vacuum UV (i.e. UV absorbed by air) andrefers to wavelengths of approximately 100-200 nm. DUV is Deep UV, andis usually used in lithography for the wavelengths produced by excimerlasers like 126 nm-248 nm. The person skilled in the art understandsthat radiation having a wavelength in the range of, for example, 5-20 nmrelates to radiation with a certain wavelength band, of which at leastpart is in the range of 5-20 nm.

FIG. 2 shows the projection apparatus 1 in more detail, including aradiation system 42, an illumination optics unit 44, and the projectionsystem PS. The radiation system 42 includes the radiation source SOwhich may be formed by a discharge plasma. EUV radiation may be producedby a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which avery hot plasma is created to emit radiation in the EUV range of theelectromagnetic spectrum. The very hot plasma is created by causing anat least partially ionized plasma by, for example, an electricaldischarge. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vaporor any other suitable gas or vapor may be required for efficientgeneration of the radiation. The radiation emitted by radiation sourceSO is passed from a source chamber 47 into a collector chamber 48 via agas barrier or contaminant trap 49 which is positioned in or behind anopening in source chamber 47. The gas barrier 49 may include a channelstructure.

The collector chamber 48 includes a radiation collector 50 which may beformed by a grazing incidence collector. radiation collector 50 has anupstream radiation collector side 50 a and a downstream radiationcollector side 50 b. Radiation passed by collector 50 can be reflectedoff a grating spectral filter 51 to be focused in a virtual source point52 at an aperture in the collector chamber 48. From collector chamber48, a beam of radiation 56 is reflected in illumination optics unit 44via normal incidence reflectors 53, 54 onto a reticle or mask positionedon reticle or mask table MT. A patterned beam 57 is formed which isimaged in projection system PS via reflective elements 58, 59 onto waferstage or substrate table WT. More elements than shown may generally bepresent in illumination optics unit 44 and projection system PS. Gratingspectral filter 51 may optionally be present, depending upon the type oflithographic apparatus. Further, there may be more mirrors present thanthose shown in the Figures, for example there may be 1-4 more reflectiveelements present than 58, 59. Radiation collectors 50 are known from theprior art.

All optical elements shown in FIG. 2 (and optical elements not shown inthe schematic drawing of this embodiment) are vulnerable to depositionof contaminants produced by source SO, for example, Sn. This is the casefor the radiation collector 50 and, if present, the grating spectralfilter 51. Hence, the cleaning method of the present invention may beapplied to those optical elements, but also to normal incidencereflectors 53, 54 and reflective elements 58, 59 or other opticalelements, for example additional mirrors, gratings, etc.

Radiation collector 50 may be a grazing incidence collector. Thecollector 50 is aligned along an optical axis O. The source SO or animage thereof is located on optical axis O. The radiation collector 50may include reflectors 142, 143, 146. These reflectors 142, 143, 146 maybe nested and rotationally symmetric about optical axis O. In FIG. 2 (aswell as in other Figures), an inner reflector is indicated by referencenumber 142, an intermediate reflector is indicated by reference number143, and an outer reflector is indicated by reference number 146. Theradiation collector 50 encloses a certain volume, i.e. the volume withinthe outer reflector(s) 146. Usually, this volume within outerreflector(s) 146 is circumferentially closed, although small openingsmay be present. All the reflectors 142, 143 and 146 include surfaces ofwhich at least part includes a reflective layer or a number ofreflective layers. On the surface of these reflective layers, there mayin addition be a cap layer for protection or as optical filter providedon at least part of the surface of the reflective layers.

The radiation collector 50 is usually placed in the vicinity of thesource SO or an image of the source SO. Each reflector 142, 143, 146 mayinclude at least two adjacent reflecting surfaces (see also FIGS. 3, 4and 6), the reflecting surfaces further from the source SO being placedat smaller angles to the optical axis O than the reflecting surface thatis closer to the source SO. In this way, a grazing incidence collector50 is constructed for generating a beam of (E)UV radiation propagatingalong the optical axis O. At least two reflectors may be placedsubstantially coaxially and extend substantially rotationally symmetricabout the optical axis O. It should be appreciated that radiationcollector 50 may have further features on the external surface of outerreflector 146 or further features around outer reflector 146, forexample a protective holder, a heater, etc.

During use, on one or more of the outer 146 and inner 142/143reflector(s) deposition may be found. The deposition may include one ormore elements selected from the group of B, C, Si, Ge and Sn, andcombinations thereof. C (carbon) may be a deposition on the radiationcollector 50 due to the undesired presence of hydrocarbons in thelithographic apparatus, but may also be deliberately present asprotective cap layer. Si (silicon) may also be deliberately present asprotective cap layer, whereas Sn (tin) may e.g. be present due to sourceSO that produces Sn, but may be deliberately present as protective caplayer. Further, Si may be present as deposition due to outgassing of theresist. The deposition may also include, for example, Mo, W, Fe, Al, Ni,Au, etc. materials that are used in, for example, the walls of theapparatus, the electrodes, gas barriers, etc.

The radiation collector 50 is deteriorated by such deposition(deterioration by debris, e.g. ions, electrons, clusters, droplets,electrode corrosion from the source SO). Deposition of Sn, for exampledue to a Sn source, may, after a few mono-layers, be detrimental toreflection of the radiation collector 50 or other optical elements,which may necessitate the cleaning of such optical elements.

Deposition, especially deposition including one or more elementsselected from the group of B, C, Si, Ge and Sn, may be removed in anembodiment by halogens (as gasses), for example, F₂, Cl₂, Br₂ and I₂and, in another embodiment by hydrogen radicals, and in yet a furtherembodiment by combinations of hydrogen radicals and one or morehalogens, either applied simultaneously or subsequently. In case thereis a deposition with e.g. Sn, or Si or Ge, due to the presence of smallamounts of oxygen, there will usually also be to some extent Sn oxideand Si or Ge oxide, respectively. To remove these oxides, a reductionstep may be necessary before elemental Sn, Si, Ge can be removed by theformation of halogenides and/or hydrides.

Removal of Radiation Collector

FIG. 3 shows an embodiment of a source collector module where theoptical axis O intersects a horizontal plane (e.g. earth) under apredetermined angle as may the case in many practical situations. Thecontaminant barrier 49 is shown to have an upstream contaminant barrierside 49 a and a downstream contaminant barrier side 49 b.

The source collector module comprises an additional, rotatablecontaminant barrier 202. The rotatable contaminant barrier 202 islocated upstream (i.e., closer to the source SO) than the contaminantbarrier 49. The rotatable contaminant barrier 202 is rotatable by amotor 204 about optical axis O. The motor 204 is connected to therotatable contaminant barrier 202 by a drive shaft 206. The motor 204 islocated partly within an opening 63 in the contaminant barrier 49 andpartly within the radiation collector 50. The radiation collector 50 isshown to be supported by the collector chamber 48 by means of asupporting structure 205, e.g. comprising a plurality of rods.

Downstream the motor 204 is connected to a hollow shaft 208 that isextending along optical axis O in order to avoid blocking portions ofthe radiation generated by source SO as much as possible. The hollowshaft 208 accommodates a plurality of cables 210 used for supplyingenergy to motor 204, to input and output sensing signals to sensors (notshown), etc. The hollow shaft 208 may also accommodate one or more ductsused for supplying or draining any desired gas to or from the interiorof the source collector module. The cables 210 are led to the exteriorof the source collector module through a sealing ring 213.

When one wishes to clean the radiation collector 50 ex-situ, i.e., at alocation exterior to the collector chamber 48, one has to remove theradiation collector 50 from the collector chamber 48. One may do so butone may be hindered to do so quickly mainly because of the followingreasons:

-   -   a. hollow shaft 208 need be removed as well as cables 210;    -   b. one must take care not to damage motor 204 or other parts,        like bearings;    -   c. one must take care that upstream radiation collector side 50        a does not damage downstream contaminant barrier side 49 b.

FIG. 4 shows an embodiment of a source collector module which isdesigned to improve ease of removal of the radiation collector 50 fromthe collector chamber 48. As a first feature, motor 204 is no longerdownstream connected to hollow shaft 208. Instead, a hollow shaft 201 isprovided upstream from radiation collector 50, accommodating cables 210,and, if desired, other components like ducts for supplying/draining gas(not shown). The hollow shaft is arranged such that it remains outsideradiation collector 50. Such a hollow shaft 201 may be a spoke ofcontaminant barrier 49. Alternatively, such cables 210 (and, if present,ducts) may be accommodated by several spokes of contaminant barrier 49.

The collector chamber 48 comprises an opening 216 that is large enoughto remove radiation collector 50 from the collector chamber 48. Thecollector chamber 48 has a flange 211 that extends from the collectorchamber 48 and defines opening 216. The flange 211 is provided with arim 207. The radiation collector 50 is connected to a support member 212which is also connected to a cover plate 214. Together, radiationcollector 50, support member 212 and cover plate 214 form a removablecollector assembly 209.

The cover plate 214 is shown as a flat plate. However, the cover plate214 may have any suitable form, e.g. may have a partial cylindricalshape. Moreover, the cover plate 214 may be designed as a load-lock.Such a load-lock may have two doors, one arranged to shut off aninternal load-lock volume from the collector chamber 48 and one to shutoff the internal load-lock volume from an external volume outside theload-lock and the collector chamber. In that external volume thecollector assembly 209 can be cleaned. When removing the collectorassembly 209 via such a load-lock the door between the load-lock and thecollector chamber 48 will be opened, and the collector assembly 209 willbe moved to the load-lock. The load-lock can be provided with the same(vacuum) pressure as the collector chamber 48 before doing so. Then, thedoor between the load-lock and the collector chamber 48 is closed,load-lock is provided with the same pressure as the external volume andthe collector assembly can be removed from the load-lock via the otherdoor between the external volume and the load-lock. With such aload-lock the internal environment (i.e. vacuum conditions) of thecollector chamber 48 is maintained as much as possible while removingthe collector assembly. For moving the collector assembly 209 back tothe collector chamber 48, such a load-lock will be used in the reversedway. A load-lock can do this all automatically, as is evident to personsskilled in the art.

In a further embodiment, such a load-lock can be one and the same as thecleaning device. Thus, then, no door to an external volume is neededanymore to perform the functions of removing and cleaning becauseremoving and cleaning will be performed by one single device.

The cover plate may seal opening 216 by a vacuum force due the vacuuminside the collector chamber 48 and non-vacuum outside collector chamber48. However, as shown in FIG. 6, cover plate 214 can be connected to therim 207 by removable connecting members 218, 220, e.g. bolts. However,other types of removable connecting members known to persons skilled inthe art may be used, e.g., all kinds of clamping devices. The connectingmembers 218, 220 and the flange 211 together with its rim 207 aredesigned such that they form a vacuum seal to opening 216 when the coverplate 214 is connected to collector chamber 48.

In the embodiment of FIG. 4, the motor 204 still extends partly intoradiation collector 50. The collector assembly 209 forms a single unitthat can, in principle, easily be removed from the collector chamber 48through opening 216. However, in order to prevent damage to motor 204and/or contaminant barrier 49, one cannot remove the collector assembly209 by a single movement in a direction perpendicular to optical axis Oonly. One way of avoiding such damage would be to first move collectorassembly 209 a first, short distance perpendicular to optical axis O (tolift cover plate 214 from the collector chamber 48), then move collectorassembly 209 downstream a second distance along optical axis O away fromsource SO and then move collector assembly 209 a third distance in adirection perpendicular to optical axis O, as indicated by arrow 215.

FIGS. 5 a-5 c shows three possible contaminant barriers 49, 49′, 49″.The FIGS. 5 a-5 c show differently shaped and oriented blades 203 allbeing oriented such that their surfaces are parallel to lines of sightoriginating from source SO. So, blades 203 do not block radiationgenerated by source SO directly. FIGS. 5 a-5 c expressly show hollowshaft 201 that is arranged for accommodating cables, ducts and the like.As mentioned earlier, the hollow shaft 201 may also have the function ofa spoke for contaminant barrier 49, 49′, 49″. Moreover, hollow shaft 201may be used as a support for motor 204. Of course, other supportingdevices, like other hollow spokes of contaminant barrier 49, 49′, 49″,may be used for supporting motor 204.

FIG. 6 shows a further improved embodiment of the source collectormodule. The arrangement is the same as the one of FIG. 4 apart from thefollowing constructive details:

-   -   a. the motor 204 has a shorter length such that it does not        extend into radiation collector 50 anymore. This allows for the        radiation collector 50 to be removed simply by removing the        connecting members 218, 220 and then moving the collector        assembly 209 outward in a direction perpendicular to optical        axis O, as indicated by arrow 215′.    -   b. both downstream contaminant barrier side 49 b and upstream        radiation collector side 50 a have flat surfaces in order to        avoid damaging contact between those surfaces during moving        collector assembly 209 outward as much as possible.

FIGS. 7 a and 7 b show different 3D views of possible embodiments of thecollector assembly 209 and the collector chamber 48. In FIGS. 7 a and 7b, the same reference numbers as used in earlier Figures refer to thesame components. In FIG. 7 a, the collector chamber 48 is connected to ahousing 218 accommodating both the source SO and (partly) contaminantbarriers 49, 202.

General Cleaning Method and General Apparatus

In an embodiment, there is provided an ex-situ cleaning methodcomprising providing a circumferential hull 500 designed tocircumferentially enclose the collector assembly 209, thereby providingan enclosure volume; providing at least one of a cleaning gas and acleaning liquid to the collector enclosure volume; and removing at leastpart of the deposition from the collector assembly 209 by the at leastone of the cleaning gas and the cleaning liquid.

Referring to FIG. 8 a, an embodiment of a cleaning device 600 isschematically depicted, with a circumferential hull 500 comprising doors120 and 130 arranged to be used as barriers at both ends 50 a and 50 b,respectively, of radiation collector 50 when it is arranged insidecircumferential hull 500), and surrounding hull 200 (which substantiallyencloses collector assembly 209). Circumferential hull 500 is designedto circumferentially enclose the collector assembly 209. This means thatcircumferential hull 500 may have every shape suitable to containcollector assembly 209. Circumferential hull 500 may be cubic,rectangular, cocoon like, etc. As shown, the cleaning device 600 has aninlet 2(1) configured to provide at least one of a cleaning gas and acleaning liquid to the enclosure volume from a gas supply or liquidsupply 6(1); and an outlet 2(2) configured to remove at least one of agas and a liquid from the enclosure volume by a drain unit 6(2).Reference number 202 refers to an optional cooling device.

In a specific embodiment, the cleaning device 600 comprises two barriers120, 130 designed to be arranged at both ends of the radiation collector50, and does not have a circumferential hull of its own. Referring toFIG. 8 b, hull 200 may be the outer surface of collector mirror 50, e.g.a surrounding outer surface of outer reflector 146. By providing twobarriers 120 and 130, like doors or shutters, at both ends 50 a and 50b, respectively, in a relatively simple way a circumferential hull iscreated, comprising the outer surface of outer reflector 146 and e.g.doors or shutters, etc. indicated in FIG. 8 b with reference symbols 120and 130, thereby providing an enclosure volume, i.e. herein the volumeenclosed by barriers 120, 130 and the outer surface of radiationcollector 50. In this embodiment, by only providing barriers 120 and 130to both ends 50 a and 50 b of radiation collector 50, an enclosurevolume is provided within outer reflector 146 and doors, shutter orother barriers 120 and 130. Hence, in an embodiment the action ofproviding circumferential hull designed to circumferentially encloseradiation collector 50 comprises providing barriers 120 and 130 to bothends 50 a and 50 b of radiation collector 50. Thus, cleaning device 600of the embodiment schematically depicted in FIG. 8 b may be a merearrangement of two barriers 120 and 130, respectively, designed toprovide a enclosure volume to radiation collector 50, and inlet(s) 2(1)and outlet(s) 2(2) to this volume for providing a cleaning liquid, acleaning gas, or both, and for removing liquid(s) or gas(ses) or both.

In yet another embodiment of the apparatus of the invention, as shown inFIG. 8 c, there is provided a cleaning device designed to receivecollector assembly 209 in its entirety The cleaning device 600 comprisescircumferential hull 500, the circumferential hull 500 comprising hull200 and doors 120 and 130. The doors 120 and 130 and hull 200 aredesigned to receive collector assembly 209, and provide circumferentialhull 500, which can be used as container for cleaning with one or moreof a gas or liquid, e.g. via gas inlet 2(1). Referring to FIG. 8 c, in aspecific embodiment this may e.g. a kind of top-loader cleaning device,with, in this embodiment, two doors 120 and 130, which can slide orotherwise be opened such that an opening is created for loadingcollector assembly 209 into cleaning device 600. After loading cleaningdevice 600, doors 120 and 130 can be closed. Cleaning device 600 mayhave any shape suitable to enclose collector assembly 209. In avariation, the embodiment as depicted in FIG. 8 c provides acircumferential hull 500 which substantially encloses collector mirror50. To this end, doors 120 and 130 may have notches such that doors 120and 130 can be arranged to circumferentially close around support member212.

In an embodiment, the cleaning device of the invention further comprisesa heating element configured to heat the enclosure volume. As describedabove, the term “a heating element” may include a number of heatingelements. Heating of the enclosure volume may be performed in differentways, e.g. in an embodiment by heating one or more of at least part ofthe enclosure volume, in an embodiment by heating the cleaning gas andin an embodiment by heating the cleaning liquid. Heating the enclosurevolume may be performed by heating the optical element, like radiationcollector 50, within the enclosure volume or by providing heatingelements within the enclosure volume of circumferential hull 500. Thus,the cleaning device could perform a vacuum baking function to providethe collector assembly with predetermined water specifications that areassociated with water specifications of the collector chamber 48.

In a specific embodiment, shown in FIG. 9, the radiation collector 50further includes one or more heating elements for heating the enclosurevolume. FIG. 9 schematically depicts a part of radiation collector 50with intermediate reflector 143 and outer reflector 146. Within a space180 between reflectors 143 and 146, there are some parts of space 180which are arranged outside the EUV radiation 35, i.e., in the shadow ofmirror 143. These parts of space are indicated by gray areas withreference numbers 32 and 34. For example, these spaces can be used toarrange filaments 110(1) and 110(2). However, these areas can also beused to arrange heating wires or tubes for transporting hot or coldfluids in order to control the temperature (not shown).

FIG. 10 schematically shows a heat source 38 controlled by a controller40. The heat source 38 may be connected to outer reflector 146 byconnectors 31. The connectors 31 may be heated conductively. Thecontroller 40 may be implemented as a suitably programmed computer, or acontroller with suitable analogue and/or digital circuits. The heatsource 38 generates heat, indicated with arrows 37, which is directed toouter reflector 146 of radiation collector 50. Heat source 38 mayinclude different heating elements and/or may be arranged such thatdifferent areas of outer reflector 146 can selectively be heated. Inthis way, removal of deposition may better be controlled. Heat source 38may be controlled by controller 40, which may amongst others alsocontrol a pump 29, or measuring devices such as thermocouples, gaspressure, gas flow, an analysis unit that analyses reflectivity ofmirror 142 and/or mirror 146, an analysis unit that measures depositionlayer thickness, etc (not shown in FIG. 10, but known to the personskilled in the art). Heaters, for example heat source 38, but alsoheating elements connected to radiation collector 50, may be selectedfrom the group of heating wires (like filaments 110(1) and 110(2) inFIG. 9), tubes containing/transporting hot fluids or hot gasses,providing hot/heated gasses to the volume to be heated, heatersconnected to or in thermal contact with radiation collector 50 (such asheat source 38 in FIG. 10) or heaters connected to or in thermal contactwith gas barriers (such as heat source 38 in FIG. 10), heating lamps(like IR lamps) and an EUV source (like source SO). The latter two maye.g. be used as preheating source.

However, in an embodiment heat source 38 may also include heatingelements on the internal surface of circumferential hull 500, either onone or more of barriers 120 and 130 and hull 200). Further, gas orliquid provided via inlet 2(1) or door 120 or 130 may also be(pre)heated by e.g. a (pre)heating device arranged between gas or liquidsupply (or pump) 6(1) and circumferential hull 500, such that theenclosure volume is heated. Hence, in an embodiment, there is provided amethod further including heating at least part of one or more selectedfrom the group of the radiation collector enclosure (such as doors 120,130, and hull 200) and cleaning gas or the cleaning liquid or both forproviding to the enclosure volume. In an embodiment, one or more heatingfilaments within the enclosure volume which can be used for heating theenclosure volume may also be used for providing hydrogen radicals fromH₂ in the H₂ containing gas (see also below).

In an embodiment, circumferential hull 500 may be construed such that akind of test tube is provided. In this embodiment, one may need only oneopening and one door 120 (or 130) for entrance of the collectorassembly, and circumferential hull 500 may be slid over the radiationcollector or the radiation collector may be slid into circumferentialhull 500, followed by closing door 120 (or 130) and the cleaning methodof the invention.

In these and other embodiments, the term “barrier” refers to doors,valves, shutters, diaphragm shutters, or other elements or devices toclose a room, space, tube, etc., and in the context of the presentinvention also to close sides 50 a or 50 b of the radiation collector50.

Herein, internal volume is the volume enclosed by the outer reflector146 and both sides 50 a and 50 b of radiation collector 50. Further,“enclosure volume” refers to this internal volume enclosed bycircumferential hull 500, wherein this volume is enclosed by outerreflector(s) 146 of radiation collector 50 and barriers 120 and 130,respectively (e.g. in case of the embodiment schematically depicted inFIG. 8 b), or to the volume provided by a circumferential hull 500,wherein this volume is enclosed by hull 200 and barriers 120 and 130,respectively (e.g. in case of the embodiment schematically depicted inFIGS. 8 a and 8 c). However, circumferential hull 500, for e.g. acleaning device as depicted in FIG. 8 a, may also have one closed end,e.g. a hull 200 integrated with “door” 130 (like a test tube), such thatthe enclosure volume in this embodiment is defined by the volumeenclosed by hull 200 and barrier 120 for the only opening for entranceof the collector assembly 209.

Referring to FIGS. 8 a, 8 b and 8 c, the gaseous or liquid cleaningmeans can be provided via supply or pump 6(1) and inlet 2(1).

Gas, either as cleaning gas or as reaction product gas(ses) (e.g. tinhydride or tin halogenide as exhaust gasses) or both (gas mixture), andliquid, either as cleaning liquid or reaction product liquid(s) or both(e.g. cleaning liquid containing reaction products) can be removed fromcircumferential hull 500, by outlet 2(2), for example by pump 6(2). Forexample, the cleaning process can be a batch or continuous process. Forexample, in case a batch process is used, outlet(s) 2(2) may not benecessary. Further, e.g. in the case of a batch process, the sides 50 aand 50 b of radiation collector 50, respectively, which are closed bybarriers 120 and 130, respectively, may also be used as gas or liquidinlet 2(1).

Pump or gas supply 6(1), pump 6(2), inlet 2(1) and outlet 2(2) may alsoinclude a number of supplies/pumps, inlets and outlets, respectively.These may be arranged and connected to hull 200, or doors 120 or 130,etc.

In an embodiment, the cleaning gas is selected from one or more of agroup consisting of a halogen containing gas and a hydrogen containinggas.

H Radical Cleaning

In an embodiment, there is provided a cleaning method wherein the gasincludes a H₂ containing gas, and wherein the method further includesproducing hydrogen radicals from H₂ from the H₂ containing gas. In thisway, the deposition is removed in the removal process by bringing thedeposition into contact with hydrogen radicals. The hydrogen radicalsmay be produced in different ways. In an embodiment, at least part ofthe hydrogen radicals are produced from H₂ from the H₂ containing gas byone or more radical formation devices selected from the group of a hotfilament, a plasma, radiation, and a catalyst configured to convert H₂into hydrogen radicals, which dissociate H₂ to H radicals or H-atomsadsorbed to the surface of the catalyst. The catalyst may includetransition metal based catalysts, for example catalysts including Pd,Pt, Rh, Ir and Ru. The catalyst may also include a Ru layer, for examplethe surface of a grazing incidence mirror or of a multilayer of theradiation collector 50, wherein Ru is included in a top layer. Theradiation for producing radicals may include radiation such as EUVradiation, DUV radiation, UV radiation, for example radiation includingradiation having a wavelength selected from the group of 193 nm, 157 nmand 126 nm, and the radiation may include radiation such as electronbeam or ionizing radiation, such that hydrogen radicals may be formedfrom hydrogen. In an embodiment, the source SO of a lithographicapparatus is used as a source SO of radiation to produce radicals. Inanother embodiment, an additional radiation source is present, toprovide such radiation that induces formation of hydrogen radicals fromhydrogen gas.

The hydrogen radicals react with contaminants like Sn (or Sn oxides), C,Si (or Si oxides), etc., leading to volatile hydrides and/or water (e.g.when an oxide like Sn oxide is reduced) that may be removed by, forexample, an exhaust. Sn and Si, that may have oxidized or which may beat least partially present as oxide as deposition or cap layer may alsobe reduced to elemental Sn and Si, respectively, and may subsequently beremoved as hydride (or as halogenide, see below). Hence, in thisembodiment, cleaning is substantially only performed with atomichydrogen to reduce and volatilize tin oxides (and/or other oxidedeposition, for example silicon oxides, on radiation collector 50) tovolatile tin hydrides (and/or other hydrides, for example siliconhydride, germanium hydride, CH₄, etc.).

In order to remove deposition on the reflectors 143 and 146 gasincluding H₂ may be provided by gas supply 6(1) through inlet 2(1) inthe space 180 where mirrors 143 and 146 of radiation collector 50 arepresent. Due to the presence of hot filament 110(1), hydrogen gasdissociates in hydrogen radicals. Part of the hydrogen radicals willcome into contact with the deposition on the surface of radiationcollector 50, where the hydrogen radicals may react with one or more ofSi (including Si oxides), Sn (including tin oxides) and C, etc. In thisway, radiation collector 50 with deposition is brought into contact withat least part of the hydrogen radicals and at least part of thedeposition is removed. Volatile compounds may be at least partially beremoved by an exhaust or pump for example as indicated with referencenumber 6(2) and 2(2), respectively. Alternatively, several supplies andseveral exhausts may be provided. Deposition removal rates of, forexample, 100-150 nm/hour can be obtained. Growth and removal rates maybe derived from ex situ X-ray fluorescence spectroscopy.

For example, after or during providing the gas to the internal volume ofthe radiation collector 50 filaments 110(1), 110(2) may be heated suchthat hydrogen radicals are formed, in the case of a hydrogen gas. Atypical temperature for filament 110(1), 110(2) is between about 1400and 2400° C. A typical temperature in the internal volume of theradiation collector 50 during treatment is between room temperature(about 20° C.) and 500° C., with a desired temperature range of about50-300° C., for example between about 100 and 200° C. Heatingfilament(s) 110(1), 110(2) as well as e.g. a heating element 38integrated in a shutter 120 or 130 (see e.g. FIGS. 9 and 10) as well asother heating elements can be used to provide this temperature.

Halogen Cleaning

Deposition, for example comprising one or more elements selected fromthe group of B, C, Si, Ge and Sn, may be removed by hydrogen radicals,but, for example, Sn may also be removed by providing halogens. Hence,in an embodiment the cleaning method further comprises providing ahalogen containing gas. In a further embodiment, there is provided amethod wherein the gas includes a I₂ containing gas, since this gasshows good results by selectively removing deposition from the surfaceof a mirror, in particular for Sn deposition, with small orsubstantially no corrosion effects to other parts of the lithographicapparatus. Hence, in this embodiment, cleaning is substantially onlyperformed with a halogen containing gas to volatilize tin (and/or otherdeposition, for example silicon on radiation collector 50) and therebyremove deposition on the radiation collector 50.

A halogen containing gas may be provided to the internal volume of theradiation collector 50 via inlet(s) 2(1) from a source 6(1). Byproviding a temperature between about 100° C. and 500° C., for examplebetween about 100° C. and 300° C., for example between about 130-200°C., the halogens form, for example, tin halogenides, thereby removing atleast part of the tin from the surface of radiation collector 50, in thecase of deposition including Sn. Heating filament(s) 110(1), 110(2) aswell as a heating element 38 integrated in a door or shutter 130, aswell as other heating elements can be used to provide this temperature.

In an embodiment, heating filaments 110(1), 110(2) may also be used toprovide halogen radicals from halogen or halogen compounds contained inthe halogen containing gas.

H Radical and Subsequent Halogen Cleaning

According to yet a further embodiment of the invention, the cleaningmethod comprises providing a H₂ containing gas; producing hydrogenradicals from H₂ of the H₂ containing gas; and subsequently providing ahalogen containing gas. In this way, the following processes may beperformed: cleaning with atomic hydrogen to reduce SnO_(x) (and/or otheroxide deposition, for example silicon oxides, on radiation collector 50)to Sn (and/or other elemental or metallic compounds, respectively, forexample Si); cleaning with a halogen, for example I₂, to remove Sn(and/or other elemental compounds, for example Si) in the form ofhalogenides, for example iodides (and/or other halogenides, for exampleSiI₄).

In a variation, the hydrogen containing gas also includes halogen gas,such that these two processes as described above are performedsubstantially simultaneously. This may be performed by a methodincluding removing at least part of the deposition from the radiationcollector 50 in a removal process including providing a H₂ and a halogencontaining gas in at least part of the enclosure volume containing theradiation collector 50; producing hydrogen radicals from H₂ from the H₂containing gas; and bringing the radiation collector 50 with thedeposition into contact with at least part of the hydrogen radicals andthe halogens in the gas and removing at least part of the deposition.The halogens may form volatile halides, and may improve the removal ofe.g. Sn and Si deposition.

H Radical/Halogen or Halogen and Subsequent H Radical Cleaning

In an above described embodiment, the cleaning method comprisesproviding a halogen containing gas. In another above describedembodiment, the cleaning method comprises providing a H₂ containing gas;producing hydrogen radicals from H₂ of the H₂ containing gas; andsubsequently providing a halogen containing gas. In yet a furtherembodiment, subsequently to providing the halogen containing gas ineither of these two embodiments, a H₂ containing gas is (again)introduced: a H₂ containing gas is (again) introduced and hydrogenradicals are produced. In this way, rests of metal halides like tinhalides and rests of halogens of the halogen containing gas (like I₂)may be removed by forming hydrides.

A gas including a combination of H₂ and a halogen may e.g. be providedby gas supply 6(1) through inlet 2(1) in the space where reflectors 143and 146 of radiation collector 50 are present.

Getter

In an embodiment one or more getter plates, getter masses or gettercoatings may be provided, on which one or more gasses selected fromhalogen gas, halogenides and hydrides may form deposits or with whichthey may react, which are then not detrimental to the other opticalelements of the lithographic apparatus anymore. For example, a Nicoating may be used to bind I₂. Such getter material may be used asseparate or as additional barrier, for example arranged on at least partof the surface of the shutters 120 and/or 130 directed to the internalvolume of radiation collector 50, or on at least part of hull 200 (seee.g. FIGS. 8 a and 8 c).

In a further embodiment, the method further includes providing a gettermaterial to the enclosure volume. Getter materials may be selected fromone or more metals selected from the group of Sn, Sb, Al, Zr, Cd, Fe,Pb, Cu, Ag and Ni, which metals may react, for example, with I₂. Forexample, Sn, Sb, Al, Zr, Cd and Fe react at about 150° C. with I₂ toform volatile products at these temperatures or higher, and Pb, Cu, Ag,Ni react at 300-500° C. with I₂ to form volatile products at thesetemperatures or higher. Getter material is provided and a coolingdevice, a heating device or both heating and cooling devices areprovided. In this way, the getter material can be maintained at thedesired temperature, i.e. below the temperature that volatilehalogenides etc. are formed (“gettering”), but the getter material mayalso be heated such that the getter can be regenerated by removal of,for example, the top layer by formation of volatile halogenides, therebyalso forming a fresh metal layer, that may subsequently be used asgetter material. The regeneration process may also be employed offline.

In an embodiment, the enclosure volume further comprises a coolingelement configured to cool at least part of the enclosure volume. Asdescribed above, the term “a cooling element” may be directed to anumber of cooling elements. In a specific embodiment, shutter(s) 120and/or 130, hull 200, maybe cooled.

In an embodiment, gettering is performed by providing and using shutters120 and/or 130 as a cold trap, to reduce the partial pressure ofhalogenides. For example, most metal iodides have a low vapor pressureat room temperature and will be trapped. Hence, in an embodiment thereis provided a method further including cooling of e.g. an exhaust gasfrom the enclosure volume. Alternatively, or additionally, at least oneselected of at least part of shutter 120, at least part of shutter 130and at least part of enclosing hull 200 may be cooled by a coolingdevice(s), suitable for cooling that part to a temperature below roomtemperature, for example suitable for cooling below 0° C., for examplesuitable for cooling in a range of −196° C. (liq. N₂ temperature) and 0°C., for example about −100° C. In yet a further embodiment, such acooling device such as a cold trap is provided to an exhaust 2(2), asschematically depicted in FIGS. 8 a and 8 b with cooling device 202.Hence, the radiation collector enclosure may further include a coolingdevice for at least part of the radiation collector enclosure. Further,in an embodiment the cleaning device 600 of the present invention mayfurther include a cooling device configured to cool an exhaust forexhaust gas from the enclosure volume. Hence, according to anembodiment, there is provided a method further comprising cooling atleast one of at least part of the enclosure volume and an exhaust gasfrom the enclosure volume.

Hence, heater 38 may also include a cooler, i.e.: reference symbol 38refers to a device for controlling the temperature and being able toheat or to cool one or more of circumferential hull 500 (e.g. barrier120, barrier 130 (if present), hull 200 (if present)), a cleaning gas, acleaning liquid, an exhaust gas (see also cooling device 202), anexhaust liquid, and a heating filament 110(1), 110(2). Heating andcooling may be controlled by controller 40.

Liquid

In an embodiment of the invention, the cleaning means comprises acleaning liquid. In a variant, the cleaning liquid comprises an etchingliquid. This liquid may comprise acids, like e.g. H₂SO₄, H₃PO₄, HF, HCL,HBr, HI, H₃BO₃, or other acids know to the person skilled in the artlike e.g. oxalic acid, acetic acid, formic acid, etc, and combinationsof two or more of these acids. The liquid may be provided via inlet(s)2(1), and the radiation collector 50 may be dipped into the liquid orthe liquid may be sprayed on the radiation collector 50 withincircumferential hull 500. The liquid may be heated before entering theenclosure volume, but may also be heated within circumferential hull500, e.g. by heating devices 110(1), 110(2) or 38. The person skilled inthe art will choose the concentration of one or more acids in an etchingliquid such that etching to a desired extent is provided. Thetemperature of the etching liquid may for example b between about −20and +150° C., and will also be chosen by the person skilled in the artsuch that etching to a desired extent is provided.

The collector enclosure may further include a cooling device for atleast part of the collector enclosure. As described above, device 38 mayalso be used in an embodiment for cooling at least part ofcircumferential hull 500, like barriers 120 and/or 130, hull 200, etc.Further, cleaning device 600 of the present invention may furtherinclude a cooling device 38 configured to cool an exhaust for exhaustliquid from the enclosure volume. Hence, according to an embodiment,there is provided a method further comprising cooling at least one of atleast part of the enclosure volume and an exhaust liquid from theenclosure volume.

Cleaning may comprise a number of cleaning steps, either a number ofliquid cleaning steps or a number of gaseous cleaning steps as describedabove, or combinations thereof, either simultaneously or subsequently.Cleaning may be monitored by measuring the performance of the opticalelement, e.g. measuring reflectivity of radiation collector 50 (see alsoabove).

Protection, Coating

Due to the aggressive media that may be used for cleaning, especiallythe liquid cleaning technique, surfaces that need not to be cleaned butwhich may be attacked by the cleaning means may be provided with aprotection. In an embodiment, the method further comprises protecting atleast one of at least part of the radiation collector and at least partof the circumferential hull 500 with a protective material. E.g. in anembodiment at least part of the circumferential hull may comprise aprotective material, or at least part of the non reflection part ofreflectors 142, 143 and 146 may comprise a protective material. In anembodiment, the protective material is e.g. a coating, like e.g. ametallic or ceramic coating, etc. In an embodiment, such protectivematerial or coating is substantially free of pinholes. In yet anotherembodiment, the layer thickness of such protective material or coatingis ≧5 μm, e.g. about 5-20 μm, in a variant about 5-15 μm.

In a variant, a coating is chosen to protect those parts of the opticalelement, like radiation collector 50, that are not optically active(i.e. e.g. the reflecting surfaces of reflectors 142, 143, 146 areoptically active, whereas the back sides of these reflectors are notoptically active). In yet a further embodiment, at least part of thecircumferential hull 500 comprises a coating, i.e. especially thoseparts of circumferential hull 500 that are exposed to a cleaning liquid.

Protection, Material

In another embodiment, the method further comprises protecting at leastone of at least part of the radiation collector and at least part of thecircumferential hull 500 by applying a material having a standardreduction potential larger than the standard reduction potential of Sn,i.e. in a variant at least part of the radiation collector or in anothervariant at least part of the circumferential hull 500 at least partiallycomprise a material or a coating having a standard reduction potentiallarger than the standard reduction potential of Sn. For example, in casea Ru mirror surface of reflectors 142, 143 and 146 is to be cleaned fromSn; the rest of the outer surface of the reflectors that may becontacted with a cleaning liquid may be protected against such cleaningliquid by a material like Au, Ir, Ag, Ru, and Rh, either e.g. as coatingmaterial or as e.g. construction material, whereas metals like Fe, Ni,etc. are avoided or otherwise protected, e.g. by a coating. Further, inyet another embodiment, the coating may be a Sn coating, e.g. having athickness of about ≧5 μm, e.g. about 5-20 μm, in a variant about 5-15μm.

Below, an overview of some materials are given, based on the reductionpotentials E° (in Volt) as derived from the Handbook of Chemistry andPhysics, 69^(th) Edition, CRC Press, Boca Raton, Fla., USA:

Reaction E° (V) Au⁺

 Au 1.692 Ir³⁺

 Ir 1.156 Pt²⁺

 Pt 1.118 Pd²⁺

 Pd 0.951 Ag⁺

 Ag 0.7996 Rh²⁺

 Rh 0.600 Ru²⁺

 Ru 0.455 Fe³⁺

 Fe −0.037 Sn²⁺

 Sn −0.1375 Ni²⁺

 Ni −0.257 In³⁺

 In −0.3382 Fe²⁺

 Fe −0.447

In a variant, a material is chosen to protected those parts of theoptical element, like radiation collector 50, that are not opticallyactive are provided with a protective material having a reductionpotential equal or larger than 0.2V. In yet a further embodiment, aprotective material having a reduction potential equal or larger than0.4V is selected. In yet a further embodiment, at least part of thecircumferential hull 500 comprises a material having a standardreduction potential larger than the standard reduction potential of Sn,i.e. especially those parts of circumferential hull 500 that are exposedto a cleaning liquid.

Protection, Voltage

In yet another embodiment, there is provided a method further comprisingprotecting at least one of at least part of the radiation collector andat least part of the circumferential hull 500 by applying a potentialsmaller than the standard reduction potential of Sn. Hence, to this endthere may in an embodiment also be provided a cleaning device furthercomprising a voltage source designed and arranged for applying apotential smaller than the standard reduction potential of Sn to atleast one of at least part of the radiation collector and at least partof the circumferential hull. Especially those parts are protected by thepotential that are not optically active, like the back sides ofreflectors 142, 143 and 146, or those parts of circumferential hull 500that are exposed to the cleaning liquid, like the internal surface ofhull 200 and/or the internal surface of doors/shutters 120 and 130.

In a specific embodiment, the voltage is at least −1.0 V, in yet afurther variant, at least −1.5 V or smaller, in even a further variant−2 V or smaller, like e.g., −3 V or smaller, −4 V or smaller, or atleast −5 V or smaller. For applying the negative potential, a voltagesupply may be used, which is connected to the surfaces which are to beprotected.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beappreciated that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, flat panel displays including liquid-crystaldisplays (LCDs), thin-film magnetic heads, etc. It should be appreciatedthat, in the context of such alternative applications, any use of theterms “wafer” or “die” herein may be considered as synonymous with themore general terms “substrate” or “target portion”, respectively. Thesubstrate referred to herein may be processed, before or after exposure,in for example a track (a tool that typically applies a layer of resistto a substrate and develops the exposed resist), a metrology tool and/oran inspection tool. Where applicable, the disclosure herein may beapplied to such and other substrate processing tools. Further, thesubstrate may be processed more than once, for example in order tocreate a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

While specific embodiments of the present invention have been describedabove, it should be appreciated that the present invention may bepracticed otherwise than as described. For example, the presentinvention may take the form of a computer program containing one or moresequences of machine-readable instructions describing a method asdisclosed above, or a data storage medium (e.g. semiconductor memory,magnetic or optical disk) having such a computer program stored therein.This computer program may be used to control the removal of thedeposition, control the pressures, control the partial pressures,control the gas flows of the gasses, control the doors/shutters 120/130,etc.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the present invention as described without departing fromthe scope of the claims set out below.

The present invention is not limited to application of the lithographicapparatus or use in the lithographic apparatus as described in theembodiments. Further, the drawings usually only include the elements andfeatures that are necessary to understand the present invention. Beyondthat, the drawings of the lithographic apparatus are schematic and noton scale. The present invention is not limited to those elements, shownin the schematic drawings (e.g. the number of mirrors drawn in theschematic drawings). Further, the present invention is not confined tothe lithographic apparatus described in relation to FIGS. 1 and 2. Thepresent invention described with respect to a radiation collector mayalso be employed to (other) multilayer, grazing incidence mirrors orother optical elements. It should be appreciated that embodimentsdescribed above may be combined. For example, more heating elements 38or hot filaments 110(1), 110(2) may be present as depicted, or may bepresent on other places as schematically depicted in the Figures.Further, gas supply and pumps, respectively, inlets and outlets,respectively, may in some cases be interchanged. For example, an inletfor providing a gas, may subsequently be used as outlet for removing agas.

1. A collector assembly comprising a radiation collector, a cover plateand a support member connecting said radiation collector to said coverplate, said cover plate being designed to cover an opening in acollector chamber.
 2. A collector assembly according to claim 1, whereinsaid support member is a plate like structure.
 3. A collector assemblyaccording to claim 1, wherein said cover plate has a flat surface.
 4. Acollector assembly according to claim 1, wherein the collector isconstructed to focus radiation emitted by a radiation source in avirtual source point.
 5. A collector assembly according to claim 1,wherein the collector is a grazing incidence collector.
 6. A collectorassembly according to claim 1, wherein the cover plate has a partialcylindrical shape.
 7. A collector assembly according to claim 1, whereinthe cover plate is designed as a load-lock arranged to shut off aninternal load-lock volume from an external volume outside the load-lock.8. A collector assembly according to claim 7, wherein the load-lock hasa door arranged to shut off the internal load-lock volume from theexternal volume.
 9. A collector assembly according to claim 1, whereinthe cover plate is designed as a load-lock arranged to shut off aninternal load-lock volume from the collector chamber.
 10. A collectorassembly according to claim 9, wherein the load-lock has a door arrangedto shut off the internal load-lock volume from the collector chamber.